furnace/hotwaterheater wont kick on

OP has already ran the stove top.

Turn on your stovetop. Got propane running through it? That is where you start.

I would think it has to be the same circuit or a propane issue. Weird how 2 systems are down. Look for whats common between them.

Furnace Fan MUST run before ANYTHING else can happen
Could be blown fuse in the DC Dist Panel.... one of those 15A fuses
Could be on/off cb switch on furnace that has tripped....manual reset
***Do you hear a CLICK AT thermostat when you set the temp higher then room temp and HEAT is selected????

Water Heater....
Could be Blown Fuse in the DC Dist Fuse Panel
The DC could be on same circuit as Furnace or another fuse
Check the 2a Fuse on Water heater circuit board in outside compartment (IF it is an Atwood ----Suburban circuit breaker is on backside of WH Tank and has no fuse)

What Brand/Model are the Furnace/Water Heater????

Yes, you can swap out fuses to different circuits.

I am usually plugged in, but when i unplug the lights are still on and bright.

You need to get a basic 12 volt DC test light.
Locate the power feed to the furnace and check for power.
If no power open the 12 volt DC fuse panel and verify that there is 12 volts leaving each of the fuses.
Are you plugged into shore power or just using battery? You said lights work. Are they bright or dim?
You may need to find a friend to help troubleshoot 12 volt power.

They have electrical igniters. I tried by turning up the thermostat(which has always worked before) and by turning on the switch for the hot water heater which has also always worked before. There is no pilot light. When i flip those switches i don't hear them clicking trying to light like i usually do. I have run the burners on the stove for a while to make sure there is gas in the lines, but it still just acts like it isn't being told to turn the HW heater and the furnace on.

How did you try lighting them? You want to make sure the propane is flowing to the systems. Sometimes it takes a while for the air to purge. Take a stick lighter and hold it in front of the pilot light. If the flame on the lighter dances, you are pushing air. If it lights up , you are getting propane. Start there.

I do not. But they are all 15 amp fuses. Can i just swap them out and try again?